1. Field of the Invention
The present invention relates to photovoltaic conversion systems, and in particular relates to photovoltaic inverters.
2. Description of the Related Art
FIG. 1 depicts a photovoltaic panel of the prior art. As shown in FIG. 1, the input terminal of an auxiliary power 12 is coupled to a photovoltaic panel 18 and the output terminal of the auxiliary power 12 is coupled to a controller 11. FIG. 2 depicts the relationship between voltage, current and power of the photovoltaic panel in different kinds of luminance of the sunlight. According to FIG. 2, the output voltage of the photovoltaic panel 18 changes in correspondence to the luminance of the sunlight. Therefore, the input terminal of the auxiliary power 12 must receive the voltage, having a wide range (such as 20 Vdc˜50 Vdc), output from the photovoltaic panel 18. But the voltage output from the output terminal of the auxiliary power 12 is fixed (e.g., 12V, 5V or 3.3V, etc). Thus, when the difference between the voltage of the input terminal of the auxiliary power 12 and the voltage which force the auxiliary power 12 to operate at a best conversion efficiency (e.g., 35V or 25V) is too much, the conversion efficiency of the auxiliary power 12 is decreased and power consumption is increased.
On the other hand, when the luminance of the sunlight is not enough (e.g., the luminance of the sunlight is lower than 100 W/m2 or the open-circuit voltage of the open-circuit voltage is lower than 40V) and the controller 11 performs a maximum power point tracking (MPPT) on the photovoltaic panel 18, the voltage output from the photovoltaic panel 18 is lower than a startup voltage (e.g., 25V) of the auxiliary power 12 such that a photovoltaic inverter 10 is turned off. Then, the controller 11 stops performing the maximum power point tracking procedure on the photovoltaic panel 18 such that the voltage output from the photovoltaic panel 18 exceeds the open-circuit voltage (e.g., 40V) of the luminance and the open-circuit voltage of the luminance is higher than the startup voltage of the auxiliary power 12, thereby turning on the auxiliary power 12 again. Because of turning on of the auxiliary power 12 again, the controller 11 performs the maximum power point tracking procedure on the photovoltaic panel 18 again such that the photovoltaic inverter 10 is turned off again. The photovoltaic inverter 10 is turned off and on repeatedly and the energy output from the photovoltaic panel 18 is not efficiently collected. Thus, there is a need for a new photovoltaic inverter to overcome such problem.